This invention relates to a semiconductor device with a multilayer wiring structure and a method of manufacturing the same and, more particularly, to an interlayer connection in the multilayer wiring structure.
The multilayer wiring structure of a conventional semiconductor device is comprised of a first wiring layer provided on a first insulating layer on a major surface of a semiconductor substrate, a second insulating layer provided over the first wiring layer and the first insulating layer, a contact hole provided in the second insulating layer such that it is positioned inside the first wiring layer, and a second wiring layer extending over the second insulating layer and connected to the first wiring layer through the contact hole. However, in such structure, the contact hole must be positioned inside the first wiring layer. As a consequence, the contact region of the first wiring layer must be made about 1.5 .mu.m larger on each side, a total of about 3 .mu.m larger on both sides, than the contact hole to accommodate the mutual positioning tolerances, the etching tolerance for the contact hole, like, and thus the wiring density of the first wiring layer is considerably reduced.
To overcome this defect in the prior art, a so-called "outward-extracted contact structure" has been proposed. The contact hole in this structure has a broader width than that of the first wiring larger so that side walls of the first wiring layer as well as its upper surface are exposed by the contact hole, and the second wiring layer is contacted to both the upper surface and side walls of the first wiring layer at the contact hole. Such a structure can improve the wiring density of the first wiring layer, because the contact hole does not need to be positioned inside the first wiring layer. However, this contact structure has the defect that a discontinuity of the second wiring layer is caused by the abrupt step at the end of the first wiring layer. Especially when the first wiring layer is made of polycrystalline silicon and the second wiring layer is made of aluminum, discontinuities occur frequently in various contact portions of the "outward-extracted contact structure".